flac: fix memory leak

Signed-off-by: Tristan Matthews <le.businessman@gmail.com>
(cherry picked from commit 52897c9020a3b8044d77866605068509924a585c)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/flac.c

@@ -418,6 +418,9 @@ static void ProcessHeader( decoder_t *p_dec )
     }
     FLAC__stream_decoder_process_until_end_of_metadata( p_sys->p_flac );
     msg_Dbg( p_dec, "STREAMINFO decoded" );
+
+    block_Release( p_sys->p_block );
+    p_sys->p_block = NULL;
 }
 
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